Clipping circuit are used to select for transimission that part of an arbitrary waveform which lie above or below some reference level.
Clipping circuit are also refered to as voltage limiters.
For an ideal diode:
  the ON state can be treated as short circuit.
  the OFF state can be treated as open circuit.
The following java applet simulate a two level clipping circuit.

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Click at one of the voltage source (DC or AC) to change its amplitude.
Left Click at hold down : decrease its value continuously
Right Click at hold down : increase its value continuously
You can also enter new value into the TextField (Double click mouse button)
Right Click mouse button to toggle the animation.
Left waveform is input signal , the right one is the output signal Red dots shows the amplitude at that time.
Yellow dots on the circuit show the flow of the current.